Resin encapsulation type semiconductor device

ABSTRACT

According to a first embodiment of the present invention, there is provided a resin encapsulation type semiconductor device, comprising a semiconductor element and an epoxy resin composition used as an encapsulating resin, the composition containing as essential components: 
     (a) an epoxy resin represented by formula (I) given below: ##STR1##  where R 1 , R 2 , R 3 , and R 4  are hydrogen or an alkyl group respectively, and n≧0, 
     (b) a phenolic resin curing agent, 
     (c) an imidazole compound, and 
     (d) triphenyl phosphate. 
     In the first embodiment of the present invention, a heat resistance skeletal structure is formed by the epoxy resin (a) and the phenolic resin curing agent (b) in the epoxy resin composition after cured, leading to an improved resistance to heat and to an improved package crack resistance. Further, the combination of the imidazole compound (c) used as a curing catalyst and triphenyl phosphate (d) permits ensuring a high reliability in terms of the humidity resistance and also permits improving the resistance to the external contamination.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resin encapsulation typesemiconductor device, in which a semiconductor element is encapsulatedwith an epoxy resin composition.

2. Description of the Related Art

A novolak type epoxy resin composition using, for example, a phenolicnovolak resin as a curing agent is excellent in its moldability. Inaddition, the composition is excellent in molding characteristics andthe cured product of that is excellent in its resistance to humidity(i.e., resistance to moisture) and electrical characteristics under hightemperatures. Thus, the composition of this type is widely used forencapsulating a semiconductor device.

In recent years, miniaturization of each functioning member of asemiconductor element and enlargement of the element itself are beingrapidly promoted in the field of a resin encapsulation typesemiconductor device in accordance with progress in the integrationdensity of the semiconductor element. As a result, required are themounting of the element at a high density and automation of theassembling process. Under the circumstances, the mounting process of asemiconductor device is being changed from the conventional pininsertion type to a surface mounting type.

The surface mounting method for mounting a semiconductor device to asubstrate is applied to, for example, the mounting of a surface mountingtype package such as a gate array called ASIC (Application Specific IC)or a standard cell type LSI. In this case, a cream solder on a substrateis heated by an infrared ray or a fluorocarbon vapor for connection to alead of a semiconductor device. In the heating step, the entire packageis exposed to such a high temperature as about 215° to 260° C. The rapidheating tends to cause crack occurrence in the package. To be morespecific, since the resin which has absorbed moisture is exposed to ahigh temperature, the water within the package is evaporated, leading toswelling of the package. Further, the stress accompanying the swellingcauses the resin to be cracked. Where the cracking reaches the outersurface of the resin (package), the reliability in terms of resistanceto humidity is markedly impaired. What should also be noted is that theresin itself is also swollen, making it impossible to achieve themounting. Still further, cracking also occurs in a PSG (phosphosilicateglass) layer or a SiN (silicon nitride) layer used as a passivation filmon a wiring layer of aluminum. Alternatively, a gold bonding wire tendsto be broken in some cases.

As described above, the reliability of the device is markedly lowered bythe crack occurrence. Presently, how to prevent the crack occurrence isa serious problem to be solved in the surface mounting process.

As a measure for solving the problem, demands are being raised forfurther improving the properties of the encapsulating resin.Particularly, when it comes to a resin encapsulation type semiconductordevice of a large package, it is demanded that the stress imparted bythe encapsulating resin to the encapsulated material be diminished, andthat the bonding strength be increased between the encapsulating resinand the PSG, SiN, and polyimide films on the surface of thesemiconductor element and between the encapsulating resin and the leadframe. It is also demanded that the encapsulating resin be imparted withsufficient strength and humidity resistance under high temperatures towhich the package is exposed in the mounting step, and that the watervapor absorption amount of the encapsulating resin be diminished.

In view of these demands, a resin composition containing apolyfunctional epoxy resin having a heat-resistant skeletal structureand/or a polyfunctional phenolic resin curing agent is proposed recentlyas an encapsulating resin having a strength high enough to withstand thewater vapor generated within the package. However, the semiconductordevice encapsulated with such a heat-resistant encapsulating resin(composition) is unsatisfactory in reliability in terms of humidityresistance and in resistance to external contamination, compared withthe device encapsulated with a novolak type epoxy resin composition.Also, the above heat-resistant encapsulating resin is poor in moldrelease characteristics. It is certainly possible to improve the moldrelease characteristics by adding a sufficient amount of a mold releaseagent. In this case, however, the bonding strength is lowered betweenthe cured resin and the semiconductor element and between the curedresin and the lead frame. It follows that, in the resin encapsulationtype semiconductor device using the above encapsulating resin, thepackage tends to be cracked in the mounting step, leading todeterioration in the reliability in terms of humidity resistance.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a resin encapsulationtype semiconductor device using an encapsulating resin excellent inheat-resistance, reliability in terms of humidity resistance, andresistance to an external contamination.

Another object is to provide a resin encapsulation type semiconductordevice without generating the package cracking and excellent inreliability in terms of humidity resistance, using as an encapsulatingresin an epoxy resin composition with improved mold releasecharacteristics and heat resistance.

According to a first embodiment of the present invention, there isprovided a resin encapsulation type semiconductor device, comprising asemiconductor element and an epoxy resin composition used as anencapsulating resin, said composition containing as essentialcomponents:

(a) an epoxy resin represented by formula (I) given below: ##STR2##where R¹, R², R³, and R⁴ are hydrogen or alkyl group respectively, andn≧0,

(b) a phenolic resin curing agent,

(c) an imidazole compound, and

(d) triphenyl phosphate or a derivative thereof.

The above epoxy resin composition used as the encapsulating resinpermits improving various properties of the resin encapsulation typesemiconductor device of the present invention. Specifically, aheat-resistant skeletal structure is formed in the cured encapsulatingresin by the epoxy resin (a) and the phenolic resin curing agent (b)contained in composition, leading to an improved heat resistance. Thecombination of the imidazole compound (c) used as a curing catalyst andtriphenyl phosphate or a derivative thereof (d) permits improving thepackage crack resistance and the resistance to the externalcontamination. Further, the combination of the components (c) and (d)permits ensuring the reliability of the cured resin in terms of thehumidity resistance. It follows that the resin encapsulation typesemiconductor device according to the first embodiment of the presentinvention exhibits a high reliability in various properties in thesurface mounting step and under various environments after the surfacemounting step. In other words, the present invention provides asemiconductor device adapted for a package of a surface mounting type.

According to a second embodiment of the present invention, there isprovided a resin encapsulation type semiconductor device, comprising asemiconductor element and an epoxy resin composition used as anencapsulating resin, said composition containing as essentialcomponents:

(a) an epoxy resin represented by formula (I) given below: ##STR3##where R¹, R², R³, and R⁴ are hydrogen or alkyl group respectively, andn≧0,

(b) a phenolic resin curing agent, and

(e) a mold release agent of a three-component system consistingessentially of an ester-based wax, an oxidized paraffin wax and anolefin-based wax.

In the second embodiment of the present invention, the mold releaseagent (e) contained in the encapsulating resin permits improving themold release characteristics of the cured resin from the mold. Inaddition, the heat resistance of the cured resin is also improved by thepresence of the epoxy resin (a) and the phenolic resin curing agent (b),as already pointed out in conjunction with the first embodiment. Itfollows that a high speed automatic molding machine can be used forstably manufacturing the device of the second embodiment. In addition, ahigh heat resistance and a high package crack resistance can be ensuredin the mounting step. Also, the device is excellent in its reliabilityin terms of humidity resistance after the mounting step. It follows thatthe semiconductor device according to the second embodiment is adaptedfor a large package of a surface mounting type.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a cross sectional view exemplifying the construction of aresin encapsulation type semiconductor device of the present invention;and

FIG. 2 is a triangular coordinate showing a preferred range of mixingratio of three components constituting a mold release agent used in thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The resin encapsulation type semiconductor device according to any ofthe first and second embodiments of the present invention can bemanufactured by, for example, encapsulating a semiconductor elementassembled by using a lead frame with an encapsulating resin by theordinary method. The device of the first embodiment is equal inconstruction to the device of the second embodiment.

FIG. 1 exemplifies a cross section of a resin encapsulation typesemiconductor device of the present invention. As shown in FIG. 1, asemiconductor chip 1 is mounted on an island 2. A plurality of bondingpads 3 are formed on the main surface of the semiconductor chip 1. Thesepads 3 are connected to a lead frame 4 via bonding wires 5. Thestructure of the particular construction Is encapsulated with resin 6 toprovide a resin encapsulation type semiconductor device.

In the first embodiment of the present invention, the encapsulatingresin 6 is formed of an epoxy resin composition containing as essentialcomponents (a) an epoxy resin, (b) a phenolic resin curing agent, (c) animidazole compound, and (d) triphenyl phosphate or a derivative thereof,as described previously. In the second embodiment, the encapsulatingresin 6 is formed of an epoxy resin composition containing as essentialcomponents (a) an epoxy resin, (b) a phenolic resin curing agent, and(e) a mold release agent of three component system consisting of anester-based wax, an oxidized paraffin wax, and an olefin-based wax.

A low pressure transfer molding is the most general method employed inthe present invention for the resin encapsulation, though it is alsopossible to employ an injection molding, compression molding, casting,etc. The epoxy resin composition is heated in the encapsulating step tocure the composition regardless of the kind of the encapsulating methodemployed. As a result, obtained is a semiconductor device having thesemiconductor element encapsulated with the cured resin. For curing thecomposition, it is desirable to apply an aftercuring treatment by theheating to at least about 160° C.

The semiconductor element is not particularly restricted in the presentinvention. Also, the type of package to be formed is not particularlyrestricted. Further, packages such as DIP and ZIP can be formed in thepresent invention in addition to the package of a surface mounting type.

The epoxy resin composition used as an encapsulating resin in the firstembodiment of the present invention comprises an epoxy resin (a)represented by formula (I), i.e., a polyfunctional epoxy resin having ahigh resistance to heat. The epoxy resin (a) can be synthesized by, forexample, epoxidizing a condensate between alkyl phenols andhydroxybenzaldehydes. The known method for synthesizing a novolak resincan be employed for manufacturing the epoxy resin (a). Specifically, inthe first step, alkyl phenols and hydroxybenzaldehydes are condensed atabout 30° to 180° C. in the presence of an inorganic acid such ashydrochloric acid or sulfuric acid, an organic acid such as acetic acid,p-toluene sulfonic acid or thioglycolic acid, or an acidic catalyst suchas Lewis acid. Then, the resultant condensate is reacted withepichlorhydrin in the presence of an alkali metal hydroxide such ascaustic soda (i.e., NaOH) to epoxidize the condensate.

It is desirable for the chlorine content of the epoxy resin to be nothigher than 1,000 ppm for ensuring the reliability of the resin. Also,an epoxy resin represented by formula (II) given below is produced bythe reaction between some molecules of the epoxy resin of formula (I):##STR4## where R¹, R², R³, and R⁴ are hydrogen or alkyl grouprespectively, and n≧0.

It follows that it is acceptable for epoxy resin (a) used in the presentinvention to contain the epoxy resin represented by formula (II).However, if the epoxy resin of formula (II) is contained in an undulylarge amount, various properties of the epoxy resin composition tend tobe degraded. Naturally, the content of the epoxy resin of formula (II)in the epoxy resin (a) should desirably be low, e.g., about 20 or less %by weight.

The epoxy resin represented by formula (I) includes, for example:

ESX-221 (trade name of epoxy resin manufactured by Sumitomo ChemicalCo., Ltd., softening point: 85° C.; epoxy equivalent: 213);

YL-6080 (trade name of epoxy resin manufactured by Yuka Shell EpoxyK.K., softening point: 90° C.; epoxy equivalent: 200); and

YL-6217 (trade name of epoxy resin manufactured by Yuka Shell EpoxyK.K., softening point: 90° C.; epoxy equivalent: 210).

An additional epoxy resin other than the epoxy resin of formula (I) canbe used together with the epoxy resin of formula (I) in preparing theepoxy resin composition used in the present invention. The additionalepoxy resin, which is not particularly restricted as far as at least twoepoxy groups are included in a single molecule, can be usedappropriately in a manner not to impair the function and effect of thepresent invention. The particular epoxy resin includes, for example, aphenolic novolak type epoxy resin, a cresol novolak type epoxy resin, anaphthol novolak type epoxy resin, a bisphenol A novolak type epoxyresin, a glycidyl ether of bisphenol A, an epoxide oftetra(hydroxyphenyl)alkane, bishydroxybiphenyl type epoxy resin, andvarious kinds of brominated epoxy resins. These additional epoxy resinscan be used singly or in combination in the present invention.

The epoxy resin composition used in the first embodiment of the presentinvention also contains a phenolic resin curing agent (b) as a componentacting as a curing agent of the encapsulating resin. It is particularlydesirable to use a phenolic resin represented by formula (III) givenbelow as the phenolic resin curing agent: ##STR5## where R⁵ and R⁶,which may be the same or different, are hydrogen or alkyl group having 1to 20 carbon atoms, and R⁷ is a single bond or an alkylene group such asmethylene or ethylene.

The phenolic resin represented by formula (III) is a condensate obtainedby the condensation reaction between, for example, phenols or aklylphenols and hydroxybenzaldehydes. The specific compounds used as thephenolic resin In the present invention include, for example,tris(hydroxyphenyl)methane, tris(hydroxymethylphenyl)methane,tris(hydroxyphenyl)propane, and tris(hydroxyphenyl)methylmethane. Thesecompounds can be used singly or in combination in the present inventionas a phenolic resin. In order to ensure reliability of the phenolicresin, it is desirable for unreacted phenol monomers to be contained inthe resin in an amount of at most 1% by weight.

The specific phenolic resins used in the present invention include, forexample:

YL-6065 (trade name of a phenolic resin manufactured by Yuka Shell EpoxyK.K., softening point: 110° C.; hydroxyl equivalent: 98);

YL-6100 (trade name of a phenolic resin manufactured by Yuka Shell EpoxyK.K., softening point: 107° C.; hydroxyl equivalent: 110);

OTM-486 (trade name of a phenolic resin manufactured by Showa HighPolymer Co., Ltd., softening point: 120° C.; hydroxyl equivalent: 98);

OTM-488 (trade name of a phenolic resin manufactured by Showa KobunshiK.K., softening point: 125° C.; hydroxyl equivalent: 98);

OTM-489 (trade name of a phenolic resin manufactured by Showa HighPolymer Co., Ltd., softening point: 123° C.; hydroxyl equivalent: 98);and

PC-7004 (trade name of a phenolic resin manufactured by SumitomoChemical Co., Ltd, softening point: 140° C.; hydroxyl equivalent: 129).

Additional phenolic resins other than those represented by formula (III)can also be used in the present invention together with the phenolicresin represented by formula (III) in a manner not to impair thefunction and effect produced by the phenolic resin curing agent (b).These additional phenolic resins are not particularly restricted as faras at least two phenolic hydroxyl groups are included in a singlemolecule. Specific examples of the additional phenolic resins include aphenolic novolak resin, a cresol novolak resin, a naphthol novolakresin, a bisphenol A novolak resin, a phenol aralkyl resin and a terpenephenol resin.

In the epoxy resin composition used in the first embodiment of thepresent invention, it is important to determine appropriately the mixingratio of the phenolic resin curing agent (b) and the epoxy resin (a).Specifically, it is desirable to set the mixing ratio of the number ofphenolic hydroxyl groups of the phenolic resin to the number of epoxygroups of the epoxy resin, i.e., the number of phenolic hydroxylgroups/the number of epoxy groups, to fall within a range of betweenabout 0.5 and 1.5. If the mixing ratio is less than 0.5, the curingreaction tends to fail to take place sufficiently, with the result thatthe cured encapsulating resin fails to exhibit a sufficiently highmechanical strength in some cases. On the other hand, if the mixingratio exceeds 1.5, the cured encapsulating resin tends to be degraded inproperties, particularly in resistance to humidity.

The imidazole compound (c) contained in the epoxy resin composition usedin the first embodiment of the present invention acts as a curingcatalyst of the encapsulating resin and, at the same time, serves toimprove the resistance to the external contamination. Specific imidazolecompound (c) includes, for example, imidazole, 2-methylimidazole,2-ethylimidazole, 1,2-dimethylimidazole, 2,4-dimethylimidazole,2-ethyl-4-methylimidazole, 2-phenylimidazole,2-phenyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole,1-cyanoethyl-2-ethyl-4-methylimidazole,2-phenyl-4,5-dihydroxymethylimidazole, and 1-vinyl-2-methylimidazole. Inorder to ensure the reliability of the encapsulating resin in terms ofthe humidity resistance, it is desirable to use an imidazole compoundhaving a long-chain alkyl group having at least 11 carbon atoms or aphenyl group bonded at the 2-position and a hydrogen atom or a methylgroup bonded at the 4-position.

The specific compounds used as the imidazole compound (c) differ fromeach other in the catalytic activity, making it difficult to determineaccurately the mixing amount of the imidazole compound (c) in the epoxyresin composition used in the present invention. However, the mixingamount of the imidazole compound (c) should desirably fall in generalwithin a range of between 0.1 to 5% by weight based on the total amountof the resin components comprising the epoxy resin (a) and the phenolicresin curing agent (b). If the mixing amount of the imidazole compound(c) is smaller than 0.1% by weight, the curing characteristics tend tobe deteriorated, leading to reduction in the heat resistance of thesemiconductor device. If the mixing amount exceeds 5% by weight,however, the reliability in terms of the humidity resistance of thesemiconductor device tends to be lowered.

It is possible for the epoxy resin composition used in the firstembodiment of the present invention to contain traces of additionalcuring catalysts together with the imidazole compound (c) describedabove in a manner not to impair the effect produced by the imidazolecompound (c). The additional curing catalysts noted above include, forexample, amine series compounds, diazabicyclo alkenes and salts thereof,organophosphines and organometallic compounds.

The specific amine series compounds which can be used in the presentinvention include, for example triethylamine, diethylenetriamine,triethylenetetramine, diethylaminopropylamine, N-aminoethylpyradine,bis(4-amino-3-methylcyclohexane)methane, metaxylyleneamine,methanediamine, and 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxospiro [5,5]undecane.

The diazabicyclo alkenes and salts thereof, which can be used in thepresent invention, include, for example, 1,8-diazabicyclo [5,4,0]undeca-7-ene and salt thereof. Further, the organophosphines used in thepresent invention include, for example, triphenylphosphine,tricyclohexylphosphine, and tris(3,5-dimethylphenyl)phosphine.

The epoxy resin composition used in the first embodiment of the presentinvention further contains triphenyl phosphate or a derivative thereof(d). Triphenyl phosphate is a compound whose chemical structure is (C₆H₅ O)₃ P=0, and the derivative of triphenyl phosphate means a compoundin which a lower alkyl group is introduced into at least one of thebenzene rings of triphenyl phosphate. The derivative includes, forexample, tricresyl phosphate (CH₃ C₆ H₄ O)₃ P=0. The component (d)serves to enable the semiconductor device encapsulated with a heatresistant epoxy resin composition to exhibit improved resistances tocracking and to humidity. The mixing amount of triphenyl phosphate (d)should fall within a range of between 0.1 and 5% by weight based on thetotal amount of the resin components of the composition. If the mixingamount of triphenyl phosphate (d) is smaller than 0.1% by weight, theepoxy resin composition tends to fail to exhibit sufficiently highresistance to humidity. On the other hand, if the mixing amount islarger than 5% by weight, the curing characteristics of the resincomposition tend to be lowered.

In addition to the essential components described above, inorganicfillers should desirably be added to the epoxy resin composition used inthe first embodiment of the present invention. The inorganic fillersused in the present invention include, for example, crushed or groundmaterials, spherical powders, fibrous materials, whiskers andmicrobaloons of quartz, fused silica, titanium oxide, silicon nitride,aluminum nitride, talc, alumina, hydrated alumina, glass, antimonyoxide, boron nitride, calcium silicate, and various ceramics. The mixingamount of these inorganic fillers is not particularly restricted in thepresent invention. However, it is desirable in general that the mixingamount of the inorganic fillers fall within a range of between 40 and75% by volume based on the total amount of the encapsulating resin. Ifthe mixing amount is smaller than 40% by volume, the thermal expansioncoefficient of the encapsulating resin tends to become unduly large,leading to reduction in the thermal shock resistance. If the mixingamount of the inorganic filler is larger than 75% by volume, however,the fluidity of the composition is lowered, with the result that themoldability of the epoxy resin composition tends to be deteriorated.

It is also possible to add a halogenated epoxy resin acting as aflame-retardant to the epoxy resin composition used in the firstembodiment of the present invention. The halogenated epoxy resin used inthe present invention is not particularly restricted as far as the resincontains halogen atoms such as bromine or chlorine atoms and at leasttwo epoxy groups in a single resin molecule. For example, it is possibleto use a bromide of a bisphenol type epoxy resin or a bromide of anovolak type epoxy resin. Preferably, used in the present invention is abrominated bisphenol type epoxy resin or a brominated novolak type epoxyresin each having a bromine content of at least 20% by weight. It ismore preferable to use a brominated bisphenol type epoxy resin having abromine content of at least 40% by weight. The specific examples of thehalogenated epoxy resin used in the present invention include:

AER-735 (trade name of a halogenated epoxy resin manufactured by AsahiChemical Co., Ltd., bromine content: 48% by weight; epoxy equivalent:350; softening point: 60° C.; semi-solid; bisphenol type);

AER-745 (trade name of a halogenated epoxy resin manufactured by AsahiChemical Co., Ltd., bromine content: 48% by weight; epoxy equivalent:400; softening point: 71° C.; bisphenol type);

AER-755 (trade name of a halogenated epoxy resin manufactured by AsahiChemical Co., Ltd., bromine content: 48% by weight; epoxy equivalent:460; softening point: 81° C.; bisphenol type);

AER-765 (trade name of a halogenated epoxy resin manufactured by AsahiChemical Co., Ltd., bromine content: 50% by weight; epoxy equivalent:602; softening point: 101° C.; bisphenol type);

BRENS (trade name of a halogenated epoxy resin manufactured by NihonKayaku Co., Ltd., bromine content: 36% by weight; epoxy equivalent: 289;softening point: 88° C.; phenolic novolak type);

Brominated EPPN 500 (trade name of a halogenated epoxy resinmanufactured by Nihon Kayaku Co., Ltd., bromine content: 44% by weight;epoxy equivalent: 285; softening point: 94° C.; phenolic novolak type);

AER-711 (trade name of a halogenated epoxy resin manufactured by AsahiKasei Kogyo K.K., bromine content: 20% by weight; epoxy equivalent: 480;softening point: 74° C.; bisphenol type);

Epiclon 152 (trade name of a halogenated epoxy resin manufactured byDai-Nippon Ink and Chemicals, Inc., bromine content: 46% by weight;epoxy equivalent: 360; softening point: 55° C.; phenolic novolak type);and

Epiclon 1120 (trade name of a halogenated epoxy resin manufactured byDai-Nippon Ink and Chemicals, Inc., bromine content: 20% by weight;epoxy equivalent: 480; softening point: 75° C.; phenolic novolak type).

Further, it is possible for the epoxy resin composition used in thefirst embodiment of the present invention to contain, as desired,suitable amounts of still additional components other than thosedescribed above, said additional components including, for example,flame-retardant assistants such as an antimony compound and a phosphoruscompound; mold release agents such as natural waxes, synthetic waxes,linear fatty acids and metal salts thereof, acid amides, esters andparaffins; coloring agents such as carbon black, titanium dioxide and adye; surface treating agents of fillers such as silane coupling agentsand titanium coupling agents; and stress-reducing agents such assilicone oil, silicone rubber, various powdery plastic materials,various powdery engineering plastic materials, and powdery ABS resin andMBS resin.

The epoxy resin composition used in the first embodiment of the presentinvention can be prepared without difficulty by employing, for example,melt kneading using a heating roll, an extruder, or a kneader, grinding,or mixing of the components with a special mixer after kneading andgrinding. Of course, some of these techniques can be employed incombination for preparing the epoxy resin composition used in thepresent invention.

An epoxy resin composition is also used as an encapsulating resin in theresin encapsulated semiconductor device according to the secondembodiment of the present invention. The epoxy resin composition used inthe second embodiment also contains the epoxy resin (a) and the phenolicresin curing agent (b), which were already described in conjunction withthe first embodiment of the present invention. The additional epoxyresin, which can be used together with epoxy resin (a) represented byformula (I) in the first embodiment, can also be used in the secondembodiment. Further, the mixing amounts of the epoxy resin and thephenolic resin curing agent (b) described previously in conjunction withthe first embodiment should also be employed in the second embodiment ofthe present invention.

The epoxy resin composition used in the resin encapsulated semiconductordevice according to the second embodiment of the present invention isfeatured in that the composition contains a mold release agent (e) ofthree component system consisting essentially of an ester-based wax, anoxidized paraffin wax, and an olefin-based wax.

To be more specific, the ester-based wax contained in the mold releaseagent (e) should desirebly be is an ester obtained by the reactionbetween a monovalent higher fatty acid and a monovalent higher alcoholand, includes, for example, carnauba wax manufactured by SoekawaRikagaku K.K., which is an ester of cerotic acid and myricyl alcohol,said ester having a melting point of 87° C., an acid value of 2 to 6,and a saponification value of 83, and Hoechst E (trade name)manufactured by Hoechst Japan Limited, which is a wax having a meltingpoint of 76° to 82° C., an acid value of 15 to 20, and a saponificationvalue of 125 to 155. Needless to say, the ester-based wax used in thepresent invention is not restricted to carnauba wax and Hoechst Eexemplified above.

The oxidized paraffin wax contained in the mold release agent (e) is anoxide of hydrocarbons, and preferably, is a mixture of higher alcohols,higher fatty acids and esters obtained by oxidizing hydrocarbons. Theoxidized paraffin wax includes, for example, LUVAX-0321 (trade name ofan oxidized paraffin wax manufactured by Nippon Seiro K.K., having amelting point of 75° C., a molecular weight of about 800, an acid valueof 12, a saponification value of 30, and a hydroxyl value of 80), andHoechst S (trade name of an oxidized paraffin wax manufactured byHoechst Japan Limited, having a melting point 78° to 84° C., an acidvalue 135 to 155, and a saponification value of 155 to 175). Of course,the oxidized paraffin wax used in the present invention need not berestricted to LUVAX-0321 and Hoechst S.

Further, the olefin-based wax contained in the mold release agent (e)should desirably be provided by a low molecular weight polyethylene anda low molecular weight polypropylene, each having a molecular weight of500 to 5,000. It is particularly desirable to use a low molecular weightpolyethylene or polypropylene modified by oxidation or acid-modified byan acid anhydride. Specific examples of the olefin-based wax used in thepresent invention are:

(1) Oxidation Type Polyethylene Wax

HW-4252E (trade name of an oxidation type polyethylene wax manufacturedby Mitsui Petrochemical Industries, Ltd., having a melting point of 93°C., a molecular weight of about 3,000, and an acid value of 17);

HW-4202E (trade name of an oxidation type polyethylene wax manufacturedby Mitsui Petrochemical Industries, Ltd., having a melting point of 101°C., a molecular weight of about 2,500, and an acid value of 17);

HW-4052E (trade name of an oxidation type polyethylene wax manufacturedby Mitsui Petrochemical Industries, Ltd., having a melting point of 110°C., a molecular weight of about 3,200, and an acid value of 20);

E-300 (trade name of an oxidation type polyethylene wax manufactured bySanyo Kasei Industries, having a melting point of 104° C., a molecularweight of about 3,000, and an acid value of 22);

E-250P (trade name of an oxidation type polyethylene wax manufactured bySanyo Kasei Industries, having a melting point of 104° C., a molecularweight of about 2,000, and an acid value of 22.);

PAD-521 (trade name of an oxidation type polyethylene wax manufacturedby Hoechst Japan Limited, having a melting point of 104° C., a molecularweight of about 2,000, and an acid value of 16); and

PAD-522 (trade name of an oxidation type polyethylene wax manufacturedby Hoechst Japan Limited, having a melting point of 104° C., a molecularweight of about 3,000, and an acid value of 25).

(2) Oxidation Type Polypropylene Wax

TS-200 (trade name of an oxidation type polypropylene wax manufacturedby Sanyo Kasei Industries, having a melting point of 145° C., amolecular weight of about 3,500, and an acid value of 3.5).

(3) Acid-Modified Type Polyethylene Wax

HW-1105A (trade name of an acid-denatured type polyethylene waxmanufactured by Mitsui Petrochemical Industries, Ltd., having a meltingpoint of 104° C., a molecular weight of about 1,500, and an acid valueof 60).

In the epoxy resin composition used in the second embodiment of thepresent invention, the mixing amount of the mold release agent (e)should desirably fall within a range of between 0.3 and 0.8% by weightin the total amount of the epoxy resin composition and within a range ofbetween 1.5 and 4.5% by weight based on the total amount of the epoxyresin and the curing agent. If the mixing amount of the mold releaseagent is smaller than the lower limits of the ranges noted above, it isdifficult to obtain satisfactory mold release characteristics in somecases. On the other hand, where the upper limits of the ranges notedabove are exceeded, the mold tends to be stained after the molding step.Also, the bonding strength between the encapsulating resin and thesemiconductor element and between the encapsulating resin and the leadframe tends to be lowered, resulting in a low reliability of the resinencapsulation type semiconductor device in terms of the humidityresistance.

FIG. 2 a triangular coordinate (i.e., triangular graph) showing adesirable mixing ratio of the three components of the mold release agent(e). As shown in FIG. 2, the mixing amounts of the three components ofthe mold release agent (e) should fall within a range defined by pointsa, b, c, d given below:

a: x=30, y=67, z=3

b: x=92, y=5, z=3

c: x=75, y=5, z=20

d: x=30, y=50, z=20

where, x denotes the ester-based wax (% by weight), y denotes theoxidized paraffin wax (% by weight), and z denotes the olefin-based wax(% by weight).

If the mixing ratio of the three components is positioned outside theline a-b and outside the line b-c shown in FIG. 2, it is impossible toobtain a sufficient effect of improving the mold release characteristicsof the resin encapsulated semiconductor device after curing of theencapsulating resin in some cases. On the other hand, if the mixingratio of the three components is positioned outside the line c-d andoutside the line d-a shown in FIG. 2, it is difficult to obtain asufficient package crack resistance in some cases.

In the resin encapsulation type semiconductor device according to thesecond embodiment of the present invention, the epoxy resin compositionmay further contain curing catalysts such as imidazole compounds, amineseries compounds, diazabicyclo alkenes and salts thereof,organophosphines and organometallic compounds as in the first embodimentdescribed previously, in addition to the essential components describedabove.

The specific compounds used as the curing catalysts in the epoxy resincomposition in the second embodiment of the present invention differfrom each other in the catalytic activity, making it difficult todetermine accurately the mixing amount of the curing catalysts. However,the mixing amount of the curing promotor should desirably fall ingeneral within a range of between 0.1 and 5% by weight based on thetotal amount of the resin components comprising the epoxy resin (a) andthe phenolic resin curing agent (b). If the mixing amount of the curingcatalyst is smaller than 0.1% by weight, the curing characteristics tendto be deteriorated, leading to reduction in the heat resistance of thesemiconductor device. If the mixing amount exceeds 5% by weight,however, the reliability in terms of the humidity resistance of thesemiconductor device tends to be lowered.

Further, the epoxy resin composition used in the second embodiment ofthe present invention may contain as desired additional addivesincluding inorganic fillers, flame-retardants such as a halogenatedepoxy resin, flame-retardant assistants, coloring agents, surfacetreating agents and stress reducing agents as in the epoxy resincomposition used in the first embodiment described previously. Theamounts of these additives should be equal to those described previouslyin conjunction with the first embodiment of the present invention.

Still further, the epoxy resin composition used in the second embodimentof the present invention can be prepared without difficulty byemploying, for example, melt kneading using a heating roll, an extruder,or a kneader, grinding, or mixing of the components with a special mixerafter kneading and grinding, as in the first embodiment describedpreviously. Of course, some of these techniques can be employed incombination for preparing the epoxy resin composition used in thepresent invention.

Let us describe more in detail the present invention with reference toExamples which follow. The following Examples are intended to facilitatethe understanding of the present invention and do not restrict thetechnical scope of the present invention.

EXAMPLES 1 TO 3 AND COMPARATIVE EXAMPLES 1 TO 3

Epoxy resin compositions were prepared by mixing the components shown inTable 1 as follows. In the first step, a filler was treated with asurface treating agent within a Henschel mixer, followed by mixing theother components of the composition and, then, kneading the mixture at60° to 130° C. by using a heating roll. The kneaded mixture was thencooled and ground so as to obtain a desired epoxy resin composition.

                                      TABLE 1                                     __________________________________________________________________________            Example                                                                            Example                                                                            Example                                                                            Comparative                                                                          Comparative                                                                          Comparative                                      1    2    3    Example 1                                                                            Example 2                                                                            Example 3                                __________________________________________________________________________    Epoxy resin                                                                   A       12.9 12.8 12.8 12.9   12.9   --                                       B       --   --   --   --     --     12.5                                     C       2.5  2.5  2.5  2.5    2.5    2.5                                      Phenolic resin                                                                (Curing agnet)                                                                A       6.2  3.1  3.1  6.2    6.2    6.5                                      B       --   3.1  3.1  --     --     --                                       Curing catalyst                                                               A       0.2  0.2  --   0.2    --     0.2                                      B       --   --   0.1  --     --     --                                       C       --   --   --   --     0.1    --                                       Mold                                                                          release agent                                                                 A       0.5  0.5  0.5  0.5    0.5    0.5                                      Pigment 0.4  0.4  0.4  0.4    0.4    0.4                                      Flame-reterdant                                                                       2.0  2.0  2.0  2.0    2.0    2.0                                      assistant                                                                     Filler  75.0 75.0 75.0 75.0   75.0   75.0                                     Surface treating                                                                      0.3  0.3  0.3  0.3    0.3    0.3                                      agnet                                                                         Triphenyl                                                                             0.1  0.1  0.1  --     0.1    0.1                                      phosphate                                                                     __________________________________________________________________________     *Numerals denote parts by weight                                         

The components of the epoxy resin compositions shown in Table 1 are asfollows:

Epoxy resin A: ESX-221 (trade name of tris (hydroxy alkylphenyl)-basedepoxy resin manufactured by Sumitomo Chemical Co., Ltd., having an epoxyequivalent of 213 and a softening point of 85° C.)

Epoxy resin B: ESCN195XL (trade name of orthocresol novolak epoxy resinmanufactured by Sumitomo Chemical Co., Ltd., having an epoxy equivalentof 197 and a softening point of 75° C.)

Epoxy resin C: AER-755 (trade name of bisphenol A type brominated epoxyresin manufactured by Asahi Chemical Industry Co., Ltd., having an epoxyequivalent of 460, a softening point of 81° C., and bromine content of48% by weight)

Phenolic resin A (curing agent): YL-6065 (trade name of atris(hydroxyphenyl)methane-based phenolic resin manufactured by YukaShell Epoxy K.K., having a hydroxyl equivalent of 98 and a softeningpoint of 121° C.)

Phenolic resin B (curing agent): BRG-557 (trade name of a phenolicnovolak resin manufactured by Showa High Polymer Co., Ltd., having ahydroxyl equivalent of 104 and a softening point of 85° C.)

Curing catalyst A: C₁₇ Z (trade name of 2-heptadecyl imidazolemanufactured by Shikoku Kasei K.K.)

Curing catalyst B: 2MZ (trade name of 2-methylimidazole manufactured byShikoku Kasei K.K.)

Curing catalyst C: PP-360 (trade name of triphenylphosphine manufacturedby KI Chemical Industry Co., Ltd.)

Mold release agent A: Carnauba No. 1 (trade name of carnauba waxmanufactured by Arakawa Rinsankagaku K.K.)

Pigment (coloring agent): CB#30 (trade name of a carbon blackmanufactured by Mitsubishi Kasei Cooperation)

Flame-retardant assistant: antimony trioxide manufactured by MikuniSeiren K.K.

Filler: fused silica powder manufactured by Toshiba Ceramics Co., Ltd.,having a crushed or ground state and an average particle size of 20microns.

Surface treating agent (coupling agent): A-187 (trade name ofy-glycidoxypropyl trimethoxy silane manufactured by Nippon Unicar Co.,Ltd.)

It should be noted that triphenyl phosphate is not contained in theepoxy resin composition for Comparative Example 1. In the epoxy resincomposition for Comparative Example 2, triphenylphosphine alone is usedas a curing catalyst. Further, an epoxy resin of the chemical structuredenoted by formula (I) is not contained in the composition forComparative Example 3.

A resin encapsulation type semiconductor device (semiconductor package)was manufactured by the ordinary method by using each of the epoxy resincompositions shown in Table 1, followed by applying evaluation tests (1)and (2) described below to each of the semiconductor packages.

1) Test for Evaluating the Humidity Resistance Reliability

A test piece device was encapsulated with each of the epoxy resincompositions, followed by applying an aftercure treatment at 180° C. for4 hours. Then, the resultant package was left to stand under anatmosphere having a temperature of 85° C. and a relative humidity of 85%so as to allow the package to absorb moisture, followed by exposing thepackage to a fluorocarbon vapor of 215° C. for one minute. The crackoccurrence of the package was examined after exposure of the package tothe fluorocarbon vapor.

Besides, the package was subjected to a pressure cooker test, in whichthe package was left to stand for a predetermined time under a saturatedsteam atmosphere of 127° C. to examine the occurrence of defectiveness(defectiveness derived from current leakage and disconnection).

2) Test for Evaluating Resistance to External Contamination

A test piece device was encapsulated with each of the epoxy resincompositions, followed by applying an aftercure treatment at 180° C. for4 hours. Then, the resultant package was dipped in a 5% aqueous solutionof sodium chloride, followed by leaving the package to stand for apredetermined time under an atmosphere having a temperature of 85° C.and a relative humidity of 85% so as to examine the occurrence ofdefectiveness (defectiveness derived from current leakage anddisconnection).

Table 2 shows the results of these tests.

                                      TABLE 2                                     __________________________________________________________________________                        Examples Comparative Examples                                                 1  2  3  1   2   3                                        __________________________________________________________________________    Cracking occurrence after                                                                  .sup.(a) Cracking                                                                    0/20                                                                             0/20                                                                             0/20                                                                             10/20                                                                             20/20                                                                             20/20                                    moisture absorption and                                                                    .sup.(b) 100 hours*.sup.1                                                            0/20                                                                             0/20                                                                             0/20                                                                              0/20                                                                             0/20                                                                              0/20                                     high temp. treatment.sup.(a) +                                                             200 hours                                                                            0/20                                                                             0/20                                                                             0/20                                                                             20/20                                                                             5/20                                                                              10/20                                    Defect occurrence after                                                                    300 hours                                                                            0/20                                                                             0/20                                                                             0/20                                                                             --  20/20                                                                             20/20                                    pressure cooker test.sup.(b)                                                               400 hours                                                                            0/20                                                                             0/20                                                                             0/20                                                                             --  --  --                                       (defective samples/all                                                                     500 hours                                                                            0/20                                                                             0/20                                                                             5/20                                                                             --  --  --                                       samples tested)                                                               Defect occurrence in                                                                       .sup.(c) 200 hours*.sup.2                                                            0/20                                                                             0/20                                                                             0/20                                                                              5/20                                                                             0/20                                                                              0/20                                     constant temp. - humidity                                                                  400 hours                                                                            0/20                                                                             0/20                                                                             0/20                                                                             20/20                                                                             0/20                                                                              0/20                                     test after dipping in                                                                      600 hours                                                                            0/20                                                                             0/20                                                                             0/20                                                                             --  0/20                                                                              0/20                                     saline solution.sup.(c)                                                                    800 hours                                                                            0/20                                                                             0/20                                                                             2/20                                                                             --  0/20                                                                              0/20                                     (defective samples/all                                                                     1000 hours                                                                           2/20                                                                             0/20                                                                             6/20                                                                             --  0/20                                                                              5/20                                     samples tested)                                                               __________________________________________________________________________     *.sup.1 Time of Pressure Cooker Test.                                         *.sup.2 Time of leaving the package to stand under the predetermined          atmosphere.                                                              

As apparent from Table 2, the semiconductor device encapsulated with theepoxy resin composition for any of Examples 1 to 3 was found to besuperior to the semiconductor device encapsulated with the epoxy resincomposition for any of Comparative Examples 1 to 3 in the resistance tocracking under high temperatures and in the humidity resistancereliability determined by the pressure cooker test conducted after thecracking resistance test. It has also been confirmed that the humidityresistance reliability is not impaired even if the epoxy resincomposition used in the present invention incurs an externalcontamination. Particularly, the combination of an imidazole compoundand triphenyl phosphate has been found to markedly improve both thehumidity resistance reliability and the resistance to externalcontamination.

EXAMPLES 4 TO 18 AND REFERENCE EXAMPLES 1 TO 4

Epoxy resin compositions were prepared by mixing the components shown inTable 3 as follows. In the first step, a filler was treated with asurface treating agent within a Henschel mixer, followed by mixing theother components of the composition and, then, kneading the mixture at60° to 130° C. by using a heating roll. The kneaded mixture was thencooled and ground so as to obtain a desired epoxy resin composition.

                                      TABLE 3                                     __________________________________________________________________________               Example 4                                                                            Example 5                                                                            Example 6                                                                            Example 7                                                                            Example 8                                                                            Example 9                       __________________________________________________________________________    Mold release agent                                                            B           0.51   0.42   0.30   0.36   0.15   0.68                           C           0.06   0.06   0.18   0.18   0.09   0.08                           D           0.03   0.12   0.12   0.06   0.06   0.04                           Epoxy resin                                                                   A          12.9   12.9   12.9   12.9   12.9   12.9                            C          2.5    2.5    2.5    2.5    2.5    2.5                             Phenolic resin                                                                (Curing agent)                                                                A          6.2    6.2    6.2    6.2    6.2    6.2                             Curing catalyst                                                               A          0.2    0.2    0.2    0.2    0.2    0.2                             Stress-reducing agent                                                         A          1.0    1.0    1.0    1.0    1.0    1.0                             B          1.0    1.0    1.0    1.0    1.0    1.0                             Filler     73.4   73.4   73.4   73.4   73.4   73.4                            Coloring agent                                                                           0.3    0.3    0.3    0.3    0.3    0.3                             Flame-retardant                                                                          2.0    2.0    2.0    2.0    2.0    2.0                             Coupling agent                                                                           0.5    0.5    0.5    0.5    0.5    0.5                             Triphenyl phosphate                                                                      0.1    0.2     0.05  0.1    0.1    0.1                             __________________________________________________________________________            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                               10   11   12   13   14   15   16   17   18                            __________________________________________________________________________    Mold release                                                                  agent                                                                         B       0.36 0.36 0.36 0.36  0.36                                                                               0.36                                                                               0.36                                                                              0.36 0.12                          C       0.18 0.18 0.18 0.18  0.18                                                                               0.08                                                                               0.18                                                                              0.18 0.36                          D       0.06 --   --   --    0.06                                                                               0.06                                                                               0.06                                                                              0.06 0.12                          E       --   0.06 --   --   --   --   --   --   --                            F       --   --   0.06 --   --   --   --   --   --                            G       --   --   --   0.06 --   --   --   --   --                            Epoxy resin                                                                   A       12.9 12.9 12.9 12.9 8.9  12.9 12.9 12.9 12.9                          C       2.5  2.5  2.5  2.5  2.5  2.5  2.5  2.5  2.5                           B       --   --   --   --   3.8  --   --   --   --                            Phenolic resin                                                                (Curing agent)                                                                A       6.2  6.2  6.2  6.2  6.4  3.1  3.1  6.2  6.2                           C       --   --   --   --   --   3.1  --   --   --                            D       --   --   --   --   --   --   3.1  --   --                            Curing                                                                        catalyst                                                                      A       0.2  0.2  0.2  0.2  0.2  0.2  0.2  --   0.2                           B       --   --   --   --   --   --   --   0.2  --                            Stress-                                                                       reducing                                                                      agent                                                                         A       1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0                           B       1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0                           Filler  73.4 73.4 73.4 73.4 73.4 73.4 73.4 73.4 73.4                          Coloring                                                                              0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3                           agent                                                                         Flame-  2.0  2.0  2.0  2.0  2.0  2.0  2.0  2.0  2.0                           retardant                                                                     assistant                                                                     Coupling                                                                              0.5  0.5  0.5  0.5  0.5  0.5  0.5  0.5  0.5                           agent                                                                         Triphenyl                                                                             0.1  0.1  0.1  0.1  0.1  0.1  0.1  0.1  0.1                           Phosphate                                                                     __________________________________________________________________________                 Reference Example 1                                                                     Reference Example 2                                                                     Reference Example 3                                                                     Reference Example                  __________________________________________________________________________                                               4                                  Mold release agent                                                            B             0.57      0.42       0.18     0.06                              C            --        --         0.42      0.54                              D             0.03      0.18     --        --                                 Epoxy resin                                                                   A            12.9      12.9      12.9      12.9                               C            2.5       2.5       2.5       2.5                                Phenolic resin                                                                (Curing agent)                                                                A            6.2       6.2       6.2       6.2                                Curing catalst                                                                A            0.2       0.2       0.2       0.2                                Stress-reducing agent                                                         A            1.0       1.0       1.0       1.0                                B            1.0       1.0       1.0       1.0                                Filler       73.4      73.4      73.4      73.4                               Coloring agent                                                                             0.3       0.3       0.3       0.3                                Flame-retardant assistant                                                                  2.0       2.0       2.0       2.0                                Coupling agent                                                                             0.5       0.5       0.5       0.5                                Triphenyl phosphate                                                                        0.1       0.1       0.1       0.1                                __________________________________________________________________________     *Numerals denote parts by weight                                         

Epoxy resins A, B, C, phenolic resin A, curing promotor A, pigment,flame-retardant assistant, filler, and surface treating agent shown inTable 3 are equal to those shown in Table 1, which were alreadydescribed in conjunction with Examples 1 to 3. The additional componentsof the epoxy resin compositions shown in Table 3 are as follows:

Phenolic resin C: YL-6065 (trade name of tris(hydroxyphenyl)methanemanufactured by Yuka Shell Epoxy K.K., having a hydroxyl equivalent of107 and a softening point of 101° C.)

Phenolic resin D: BRG-556 (trade name of a phenolic novolak resinmanufactured by Showa High Polymer Co., Ltd., having a softening pointof 85° C.)

Stress reducing agent A: BTA-731 (trade name of methylmethacrylate-butadiene-styrene copolymer manufactured by Kureha ChemicalIndustry Co., Ltd.)

Stress reducing agent B: TSJ-3051 (trade name of an additionthermosetting silicone gel manufactured by Toshiba Silicone Co., Ltd.,having a viscosity of 1,000 cP at (25° C.)

Mold release agent B: Carnauba No. 1 (trade name of an ester-based waxmanufactured by Soekawa Rikagaku K.K., having a melting point of 87° C.,an acid value of 2 to 6, and a saponification value of 83)

Mold release agent C: Calbacks 0321 (trade name of an oxidized paraffinwax manufactured by Nippon Seiro K.K., having a melting point of 75° C.,a molecular weight of about 800, an acid value of 12, a saponificationvalue of 30, and a hydroxyl value of 80)

Mold release agent D: HW-4252E (trade name of an oxidation modifiedpolyethylene wax manufactured by Mitsui Petrochemical Industries, Ltd.,having a melting point of 93° C., a molecular weight of about 3,000, andan acid value of 17)

Mold release agent E: E-250P (trade name of an oxidation modifiedpolyethylene wax manufactured by Sanyo Chemical Industries Ltd., havinga melting point of 104° C., a molecular weight of about 2,000, and anacid value of 20)

Mold release agent F: HW-2203A (trade name of an oxidation modifiedpolyethylene wax manufactured by Mitsui Petrochemical Industries Ltd.,having a melting point of 107° C., a molecular weight of about 2,700,and an acid value of 30)

Mold release agent G: TS-200 (trade name of an oxidation modifiedpolyethylene wax manufactured by Sanyo Chemical Industries having amelting point of 145° C., a molecular weight of about 3,500, and an acidvalue of 3.5)

It should be noted that at least one of mold release agents B, C and Dis not contained in the epoxy resin compositions for Reference Examples1 to 4. On the other hand, all of these mold release agents B, C, D arecontained in the epoxy resin composition for Example 8. In this case,however, the mixing ratio of these three mold release agents does notfall within the range a-b-c-d shaded in the triangular coordinate ofFIG. 2.

Evaluation tests 3) to 5) were applied as follows to these epoxy resincompositions so as to evaluate the resin encapsulation typesemiconductor device manufactured by using these epoxy resincompositions:

3) Bonding Strength with Lead Frame made of 42 Alloy

A molded product of each of the epoxy resin compositions was formed on asurface, having an area of 4 mm², of a lead frame made of 42 alloy,followed by applying an aftercure treatment to the molded body at 175°C. for 8 hours so as to prepare a test piece. Then, each of the testpieces was subjected to a moisture absorption treatment for 168 hours at85° C. under a relative humidity of 85%. After the moisture absorptiontreatment, the bonding strength was measured between the resin moldedproduct and the lead frame made of 42 alloy. Table 4 shows the results.

4) Residual Rate of Lead Frame within Mold

A lead frame was encapsulated with each of the epoxy resin compositionsby using a low pressure transfer molding machine. The moldingtemperature was set at 175° C. and the molding was performed for 2minutes. A similar encapsulating process was performed for 50 shots foreach of the resin compositions, followed by releasing the encapsulatedlead frame from the mold by the ordinary method so as to measure theresidual rate of the lead frame within the mold. Table 4 also shows theresults.

5) Crack Occurrence after VPS Treatment

A semiconductor element having a chip size of 15 mm was encapsulatedwith each of the epoxy resin compositions by using a low pressuretransfer molding machine. The molding temperature was set at 175° C. andthe molding was performed for 2 minutes. Then, an aftercure treatmentwas applied to the resin encapsulated semiconductor element at 175° C.for 8 hours so as to manufacture a flat package (i.e., resinencapsulation type semiconductor device) having 184 pins. Further, theresultant flat package was subjected to a moisture absorption treatmentat 85° C. under a relative humidity of 60% for 168 hours, followed byapplying a vapor phase reflow (VPS) treatment at 215° C. to the packageso as to examine the occurrence of defective packages by measuring thecrack occurrence reaching the outer surface of the package immediatelyafter the VPS treatment.

Besides, the package was subjected to a humidity resistance reliabilitytest in which the package was left to stand for a predetermined time ina pressure cooker of 121° C. and 2 atm. to examine the occurrence ofdefectiveness. Table 4 also shows the results.

                                      TABLE 4                                     __________________________________________________________________________                 Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                          4    5    6    7    8    9    10   11   12   13                  __________________________________________________________________________    Bonding strength with lead                                                                 1.5  1.4  1.0  1.2  1.9  0.8  1.3  1.4  1.2  1.2                 frame (kg/mm.sup.2)                                                           Lead frame residual rate                                                                   0    0    0    0    0    0    0    0    0    0                   in mold (%)                                                                   Crack occurrence after                                                                     0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20                VPS treatment (cracked                                                        samples/all samples tested)                                                   Humidity resistance                                                           reliability test                                                              (defective samples/all                                                        samples tested)                                                                40H         0/20 0/20 0/20 0/20 2/20 0/20 0/20 0/20 0/20 0/20                 80H         0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20                160H         0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20                320H         0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20 0/20                500H         0/20 0/20 0/20 0/20 0/20 1/20 0/20 0/20 0/20 0/20                __________________________________________________________________________                 Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                             Reference                                                                           Reference                                                                           Reference                                                                           Reference                         14   15   16   17   18    Example 1                                                                           Example 2                                                                           Example                                                                             Example              __________________________________________________________________________                                                             4                    Bonding strength with lead                                                                 1.3  1.4  1.5  1.3  1.0   1.5   0.5   1.0   0.6                  frame (kg/mm.sup.2)                                                           Lead frame residual rate                                                                   0    0    0    0    0     20    0     16    6                    in mold (%)                                                                   Crack occurrence after                                                                     0/20 0/20 0.20 0/20 1/20  0/20  9/20  0/20  5/20                 VPS treatment (cracked                                                        samples/all samples tested)                                                   Humidity resistance                                                           reliability test                                                              (defective samples/all                                                        samples tested)                                                                40H         0/20 0/20 0/20 0/20 0/20  0/20  0/20  0/20  0/20                  80H         0/20 0/20 0/20 0/20 0/20  0/20  0/20  0/20  0/20                 160H         0/20 0/20 0/20 0/20 0/20  0/20  3/20  0/20  1/20                 320H         0/20 0/20 0/20 0/20 1/20  0/20  6/20  0/20  2/20                 500H         0/20 0/20 0/20 0/20 2/20  0/20  7/20  2/20  6/20                 __________________________________________________________________________

As apparent from Table 4, the epoxy resin compositions for Examples 4 to18 were superior to the compositions for Reference Examples 1 to 4 inthe bonding strength of the molded product with the lead frame made of42 alloy. Also, a residual lead frame within the mold was not found inthe Examples of the present invention, indicating that the epoxy resincomposition defined in the present invention exhibits excellent moldrelease characteristics. Further, crack occurrence was suppressed evenafter the VPS treatment when it comes to the resin encapsulation typesemiconductor device of the present invention manufactured by using theepoxy resin composition defined in the present invention. Still further,the resin encapsulation type semiconductor device of the presentinvention was found to exhibit an excellent performance in the humidityresistance reliability test conducted after the cracking resistancetest. It follows that the resin encapsulation type semiconductor devicecorresponding to any of Examples 4 to 18, which are excellent in themold release characteristics in the manufacturing process, permitsimproving the manufacturing efficiency of the device and enables themanufactured device to exhibit a satisfactory reliability in terms ofits resistance to humidity.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A resin encapsulation type semiconductor device, comprising a semiconductor element encapsulated with an epoxy resin composition, said composition containing as essential components:(a) an epoxy resin represented by formula (I) given below: ##STR6## where R¹, R², R³, and R⁴ are hydrogen or an alkyl group respectively, and n≧0, (b) a phenolic resin curing agent, (c) an imidazole compound, and (d) triphenyl phosphate or a derivative thereof.
 2. The resin encapsulation type semiconductor device according to claim 1, wherein said epoxy resin composition further contains an inorganic filler.
 3. The resin encapsulation type semiconductor device according to claim 1, wherein said epoxy resin composition further contains an epoxy resin having a chemical structure differing from that of said epoxy resin (a).
 4. The resin encapsulation type semiconductor device according to claim 1, wherein said phenolic resin curing agent (b) is a phenolic resin represented by formula (III) given below: ##STR7## where R⁵ and R⁶, which may be the same or different, are hydrogen or an alkyl group having 1 to 20 carbon atoms, and R⁷ is a single bond or an alkylene group.
 5. The resin encapsulation type semiconductor device according to claim 1, wherein the mixing ratio of said epoxy resin (a) and said phenolic resin curing agent (b) contained in said epoxy resin composition falls within a range of between about 0.5 and 1.5 in terms of the ratio of the number of the phenolic hydroxyl groups of the phenolic resin to the number of epoxy groups of said epoxy resin.
 6. The resin encapsulation type semiconductor device according to claim 1, wherein said imidazole compound (c) is an imidazole compound having a long chain alkyl group having at least 11 carbon atoms or a phenyl group bonded at 2-position and hydrogen or a methyl group bonded at 4-position.
 7. The resin encapsulation type semiconductor device according to claim 1, wherein said imidazole compound (c) is contained in the epoxy resin composition in an amount of about 0.1 to 5% by weight based on the total weight of the resin components comprising the epoxy resin (a) and the phenolic resin curing agent (b).
 8. The resin encapsulation type semiconductor device according to claim 1, wherein said triphenyl phosphate or a derivative thereof (d) is contained in the epoxy resin composition in an amount of about 0.1 to 5% by weight based on the total weight of the resin components comprising the epoxy resin (a) and the phenolic resin curing agent (b).
 9. A resin encapsulation type semiconductor device, comprising a semiconductor element encapsulated with an epoxy resin composition, said composition containing as essential components:(a) an epoxy resin represented by formula (I) given below: ##STR8## where R¹, R², R³, and R⁴ are hydrogen or an alkyl group respectively, and n≧0, (b) a phenolic resin curing agent, and (c) a mold release agent of a three-component system consisting essentially of an ester-based wax, an oxidized paraffin wax and an olefin-based wax.
 10. The resin encapsulation type semiconductor device according to claim 9, wherein said epoxy resin composition further contains an imidazole compound as a curing catalyst.
 11. The resin encapsulation type semiconductor device according to claim 9, wherein said epoxy resin composition further contains an inorganic filler.
 12. The resin encapsulation type semiconductor device according to claim 9, wherein said epoxy resin composition further contains an epoxy resin having a chemical structure differing from that of said epoxy resin (a).
 13. The resin encapsulation type semiconductor device according to claim 9, wherein said phenolic resin curing agent (b) is a phenolic resin represented by formula (III) given below: ##STR9## where R⁵ and R⁶, which may be the same or different, are hydrogen or an alkyl group having 1 to 20 carbon atoms, and R⁷ is a single bond or an alkylene group.
 14. The resin encapsulation type semiconductor device according to claim 9, wherein the mixing ratio of said epoxy resin (a) and said phenolic resin curing agent (b) contained in said epoxy resin composition falls within a range of between about 0.5 and 1.5 in terms of the ratio of the number of the phenolic hydroxyl groups of the phenolic resin to the number of epoxy groups of said epoxy resin.
 15. The resin encapsulation type semiconductor device according to claim 9, wherein said ester-based wax acting as one component of the mold release agent (e) is an ester obtained by the reaction between a monovalent higher fatty acid and a monovalent higher alcohol.
 16. The resin encapsulation type semiconductor device according to claim 9, wherein said oxidized paraffin wax acting as one component of the mold release agent (e) is a mixture of higher alcohols, higher fatty acids and esters, said mixture being obtained by oxidizing a hydrocarbon.
 17. The resin encapsulation type semiconductor device according to claim 9, wherein said olefin-based wax acting as one component of the mold release agent (e) is a low molecular weight polyethylene or a low molecular weight polypropylene each having a molecular weight of 500 to 5,000.
 18. The resin encapsulation type semiconductor device according to claim 9, wherein the mixing ratio of said ester-based wax, said oxidized paraffin wax and said olefin-based wax, which collectively form said mold release agent (e), is: 30≦x≦92, 5≦y≦67, 3≦z≦20, and x+Y+z=100, where x denotes the percentage by weight of the ester-based wax, y denotes the percentage by weight of the oxidized paraffin wax, and z denotes the percentage by weight of the olefin-based wax.
 19. The resin encapsulation type semiconductor device according to claim 9, wherein said mold release agent (e) is contained in the epoxy resin composition in an amount of 0.3 to 0.8% by weight in the amount of the epoxy resin composition and in an amount of 1.5 to 4.5% by weight based on the total amount of the epoxy resin and the curing agent contained in the composition.
 20. A resin encapsulation type semiconductor device, comprising a semiconductor element encapsulated with an epoxy resin composition, said composition containing as indispensable components:(a) an epoxy resin represented by general formula (I) given below: ##STR10## where R¹, R², R³, and R⁴ are hydrogen or an alkyl group respectively, and n≧0, (b) a phenolic resin curing agent, (c) an imidazole compound, (d) triphenyl phosphate or a derivative thereof, and (e) a mold release agent of a three-component system consisting essentially of an ester-based wax, an oxidized paraffin wax and an olefin-based wax. 